Sun Ce, to put it nicely, is described as "a man of good looks, with a good sense of humor, open-minded and tolerant, skilled at employing people." To be blunt, it means he acts without thinking. If he trusts you, he really trusts you.
If he calls you a brother, he truly treats you like a brother. His thinking is so peculiar that it's on a completely different wavelength from normal people.
So, after the Northern Huns moved southward, Sun Ce, like most of the feudal lords in the Central Plains, also thought of launching a northern expedition. However, his unique way of thinking meant he couldn't be as meticulous as Cao Cao or Liu Bei. Upon receiving the news, he headed north directly.
As for troops, Sun Ce didn't bring any. In his mind, there have been so many times when he was just traveling and some people would arrive with their troops to join him. Besides, even if no one brought troops to join him, doesn't he have a buddy named Ma Chao?
